Method of electrical signaling



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UNITED STATES;

WILLIAM F. FRIEDMAN, OF WASHINGTON, DISTRICT OF COLUMBIA.

METHOD OF ELECTRICAL SIGNALING.

Application filed. July 10, 1922. Serial No. 573,981.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED 623112 30, 1928; 370 0. G. 757.)

This invention relates in general to elec-- trical signaling systems and more particularly to systems for the simultaneous transmission of a plurality of messages through one and the same channel, and has for its object the provision of a new and more simple system of circuits for achieving this end.

A further object of the invention is to effect a reduction of the length of time necessary to transmit and receive each of a plurality of messages by the heretofore prevalent systems of multiplex printing telegraphy, and thus increase the capacity of a single channel.

A further object is-to effect an increase in a the number of telegraph messages which can be transmitted over a single channel by the heretofore prevalent systems of multi- I plex telegraphy. a

A further object is to achieve a system of -multiplex radio telegraphy by the use of a single wave instead of a plurality of waves of different frequencies.

The fundamental principle of my 1nvention is the differential modulation of a single.

carrier wave and the selective isolation of the several modulating frequencies at the In order that the inventionand its mode -of application may be readily understood by persons skilled in the. art, I have, in the accompanying illustrative drawings, and in the detailed following description based thereon, set forth an embodiment of the same.

waves are first separated bytuning to the frequencies of the carrier waves and then tuning again to the modulating frequencies.

Figures 3 and 4 are the same as Figures 1 and 2, respectively, except that the arrangements in Figures 3 and 4 are adapted for radio transmission instead of line transsource of high frequency oscillations of constant'frequency, designated hereafter as the carrier wave; 'B and C are arrangements for modulating the carrier wave, each differently modulating the carrier wave A; D and E are keys which respectively-control the modulation elements B and C. These keys may be' operated manually by individual operators employing the Morse code signals but as shown in the figure they are here illustrated as operatively connected to I, which isa sending keyboard oran automatic tape-controlled transmitter, both of well known form. F and F constitute the line which the carrier wave traverses. and. C are selectively tuned circuits responsive to the carrierwave A; D and E rep;-

resent circuits selectively tuned to respond individually to the respective modulating frequencies; G and H are relays which may be of well known forms, and are operable by the currents passed by D and E respectively, but they may be any other form of device suitable for making'the currents of the isolated frequencies perceptible to the eye or car, or for recording these currents in a suitable manner. The figure, however, shows G and H to be relays operatively con nected to J, a printing or recording deviceof any of the well known forms.

Let us suppose that A impresses upon the line F-F a carrier wave of 50000 cycles per second, that B modulates the carrier wave by 1000 cycles per second and that C modulates the carrier wave by 2000 cycles per second. Therefore a carrier wave modulated in one instance to a 49000-51000 cycle wave, and in the other instance to a 48000- 52000 cycle wave is impressed upon-the line.

At the receiving'end of the line B and 0 other will be acted upon only by the 2000 v can be placed at both ends of the line, and y cycle modulating frequency. In that way the different modulating frequencies are separated. Hence relays G and H will respond selectively to the modulating frequencies of B and C. v

The tuning of the receivers B and C to a modulated wave which covers a narrow band of frequencies as in the preceding example, 49000 to 51000 cycles or 48000 to. 50000 cycles, may be accomplished by thewell known methods in the art, which may be by the use of band filters, or any other suitable circuit arrangements.

In the same way a plurality of carrier waves of different frequencies may be employed, each carrier wave separately modulated by several modulations of different characters, and at the receiving end the different frequency carrier waves are first separated by suitable tuning and by further tuning the individual modulating frequencies on each carrier wave may be isolated. Thus a multiplex system of extremely wide range is made possible. This is shown diagrammatically in Figure 2, where A represents one unit of carrier wave current of on frequency from source C, with its associated -modulating frequencies D and E, and B represents another unit of carrier wave current of another frequency from source F, with its associated modulating frequencies, G and H. A represents a system of circuits comprising circuitsv C and C selectively tuned ,to the frequency of the carrier wave C, and circuits D and E, selectively tuned to the modulating frequencies D and E, which ar'eproduced at A, and I, J, are relays actuated by circuits D, E,,respectively. B represents a system of circuits comprising circuits F and F selectively tuned to the frequency of the carrier wave, F, and circuits G and H, selectively tuned. to the.

modulating frequencies, G and ,H, which' are produced at 'B,-and K, L are relays actuated by circuits G, H, respectively. M, N, O, and P are the ke s controlling the modulating circuits at A and B, and Q, Q

is the line. p I It is obvious also that transmitting sets their corresponding receiving sets at both ends of the line, so that multiplex operation is possible. For such operation a plurality of sin le period generators or a single multiperio generator can be employed. This arrangement is especially adapted for print- "the operation of a particular rela ing telegraph systems which employ code signals consisting of a plurality 0 elements or units affecting a plurality of relays associated with a printing or a recording mechanism. It maybe desirable to discuss briefly this aspect-of the invention.

In the heretofore prevalent forms of print ing telegraph systems, the automatic operations concerned in causing a printing mechanism to function at a distance are controlled by groups of equal potential, direct current electrical impulses which pass over one and t e sameline, and actuate a set of relays, ea h impulse in the group effecting method described below. These re ays ac tuate magnets which set up combinations of selecting discs in a printing mechanism, and each character of'the message is determined by a different combination or arrangementof these selecting discs. Usually there are 32 such combinations, 26 for the ordinaryletters and 6 others concerned in certain functions of the printer, such as carriage return, figure shift, and so on. The signals for message characters ascommonly. used in these systems constitute what is usually ,by atermed a five-unit code, that is, it consists of permutations of two elements taken five at a time. In one system of operation these two elements may be positive and negative potentials, in which case the code signal for a character consists of the distribution through time of five elements composed of positive and negative impulses. In another system of operation the two elementsmay consist of a time-interval when an impulse is sent, and a time-interval when no im ulse is sent, this being the method of. close and open circuit operation. The code signal for the letter A for example, is which in the positive and negative system of operation means -that the first and second units of the signal are positive impulses, the third, fourth, and fifth, are negative impulses. In the open and closed circuit system of operation, this code signal means that only the first" two time units are occupied by the passage of current, the last three, unoccupied. The permutations of transmitted impulses are governed by a set of make and break keys operated at the transmitting end manually, by means of a sending keyboard similar in form to the ordinary typewriter keyboard, or automatically by means of a transmitter controlled by a perforated tape.

In order that a plurality of relays shall established between each key atthe sending end and its corresponding relay at the receiving end at a-difl'erent instant, and the several connections necessary to transmit the code signal for each messagecharacter are interval, connection is established between key 2 at the sending end and its corresponding relay 2 at thereceiving end, and so on. The method of effecting such a correspondence in action by transmitting similar impulses through one and the same channel involves the use of a distributor and various other apparatus included under the general term synchronizing mechanism.

The principal of the synchronizing distributor is this: two similar rings, one, on the sending face of a distributor at the transmitting station, the other on the receiving face of an identical distributor at the receiving station, are each divided into five equal segments. A pair of rotating brushes on these distributors are connected to the line, and when these brushes revolve they sweep over and make contact with the segments of their respective rings. The brushes at the two ends of the line start from the same relative position and sweep over the contact segments with the same uniform angular velocity, thus connecting the first segment of the ring of the sending distributor with the first segment of the ring of the receiving distributor once per revolution of the brushes." Likewise the second, third, fourth, and fifth segments of the sending distributor are connected once per revolution of the brushes with the corresponding segments of the'receiving distributor, the interval of each connection being the time of one-fifth of a revolution of the rotating bnushes. Thus, each message character is transmitted as a combination of five separate or discrete impulses distributed equally and in a definite sequence through an interval of time, and for each revolution of the brushes, the code impulse combinations for one and only one character or letter are transmitted and received. The synchronization of the two distributors so that the respective brushes revolvewith exactly the same angular velocit is a very complex feature of these rintmg telegraph systems, and acts as a limiting factor upon the speed of operation. In my system no such synchronization is necessary, for all of the signals comprising the combination of impulses for a single character are transmitted simultaneously, and at the receiving end are circuits.

There is, of course, nothing novel in modu lating a carrier wave either telephonically or telegraphically. The novelty of my invention consists in modulating a single carrier wave telegraphically by several distinct modulating frequencies,.and isolating each modulating frequency individually. In telephonic modulation a relatively wide band of modulating frequencies is imposedupon the carrier wave, and this band of heterogeneous side frequencies is faithfully reproduced by the telephone receiver at the receiving end. The human ear hears all of these heterogeneous side frequencies simultaneously, but is able to distinguish them and hear them separately if an effort isv made. For example, when orchestral music is being transmitted by radio telephone, the radio audience hears the ensemble effect but there is absolutely no dif ficulty in distinguishing the music produced by a violin from that produced by a cornet. Both sounds are being transmitted on one and the same vehicle or carrier wave, but the modulating frequency of the sound vibrations of the violin is different from that of the cornet. While in the illustration given above the separation of the modulating frequencies is effected by the ear, in the arrangement of this invention the separation properly isolated by five selectively tuned of the modulating frequencies is accomplished by mechanical or electrical tuning devices;

In Figure 3 the arrangements of circuits A is identical with that shown in Figure 1,

but instead, of having a line upon which the modulated carrier waves are impressed, a' transmittingantenna, F, with itsground'I, serves to radiate the modulated waves into space, and a receiving antenna F with its ground I, serves to receive the waves radiated by F In Figure 4, the arrangement of circuits is identical with that shown in Figure 2, but instead of having a line upon which the modulated carrier waves are impressed, a transmitting antenna, Q, with'its ground R, serves to radiate the modulated waves into space, and a receiving antenna, Q, with its ground, It, serves to receive the waves radiated by Q.

It is obvious that the arrangements shown in Figure 1 for controlling the operationof the keys governing the modulating circuits and for controlling the operation of the printing or recording mechanism, when a system of printing telegraph is employed, also apply to Figures 2, 3, and 4. But it also obvious that the modulating keys may be operated manually by individualoperators, as stated before, and at the receiving end, instead of having relays, several operators may receive the messages transmitted in ordinary Morse characters by using telephone receivers.

' It is obvious that radio-frequency oscillations must be employed for radio communication by the systems illustrated in therier waves are impressed on the line or radi.

ated into space, it is to be understood that any of the means and methods now well known in the art may be employed. Nor have Iindicated any details with respect to the exact means to be used in receiving the modulated carrier waves, selectively separating the modulating frequencies, and causing them to affect selectively tuned relays or recording devices, for here also the means and methods now well known in the art apply to this invention.

What I claim as my invention is the following:

1. In a printing telegraph system, a source of high frequency electrical oscillations constituting a carrier wave, a set of modulators of different modulating frequencies which can be impressed upon said carrier wave, each of said modulators being associated with a make and break key which determines whether the modulating frequency controlled thereby will or will, not be impressed upon the said carrier wave, said keys together comprising a single set of keys acting as a single unit associated with a keyboard mechanism, said keyboard mechanism being so constituted as to control said set of keys permutatively as a unit according to a plural-unit code suitable for the representation of message characters, means for transmitting the permutatively modulated carrier wave representing the message characters, a receiving station, means at said receiving station for detecting said transmitted permutatively modulated carrier wave, means for detecting the presence of and for isola'ting each modulating frequency of said ermutatively modulated carrier wave, said atter means comprising a set of resonant circuits appropriatefor the purpose, each of said resonant circuits being associated with and adapted to control a relay ,which is operative when the modulating frequency to which the respective resonant circuit is res onsive is present, and is inoperative when tiie modulating frequency to which said resonant circuits is responsive is not present, a plurality of relays acting, as a single unit associated with a printing mechanism, said printing mechanismbeing controlled as a unit by the joint and permutative action of said set of relays in such a manner as to print the message charactersrepresented by message characters, a set of resonant circuits, each of said resonant circuits being responsive to one individual and only one of said modulating frequencies, a set of rela s controlled as a unit permutatively by t e said set of resonant circuits, and a printing mechanism controlled by the said set of relays and suitable for printing the received message characters, themethod of permutatively and simultaneously impressing the said modulating frequencies u on the said carrier wave, transmitting an subsequent receiving and detecting the said permutatively modulated carrier wave, detecting and isolating the said modulating frequencies, causing the said isolated modulating frequencies to control the operation of a set of relays permutatively according to the pluralunit code representing the message characters transmitted, the said set of relays acting as a unit to control the actionof a printing mechanism suitable for characters. 4

In testlmony whereof I afiix my signature,

WILLIAM F. FRIEDMAN.

printing the message 

